Britain's new representative in Brussels will be put in charge of tackling terrorism across the European Union.

Sir Julian King is being made Commissioner for the Security Union in a surprise move by the executive's president, Jean-Claude Juncker.

The outgoing UK ambassador to France was not expected to be handed a high profile portfolio given Britain's vote to quit the bloc.

Security is a "pressing challenge" and the wave of terror attacks in France, Germany and Brussels underline the need for "swift progress", Mr Juncker said.

Sir Julian will be expected to come up with "concrete" action to tackle terrorism, prevent radicalisation, disrupt organised crime and fight cybercrime, he added.

The new commissioner has been tasked with drawing up measures to deal with returning foreign terrorist fighters, improving information and intelligence sharing and boosting protection for critical infrastructure and soft targets.

Sir Julian, whose appointment on the commission must be approved by MEPs, will report to a series of vice-presidents who form Mr Juncker's top team.

Despite the Brexit vote, the UK remains a full member with the right to one of the 28 seats on the powerful Commission until it has formally left the EU.

Mr Juncker said all commissioners must be "very determined and very responsible" in their work and must only have the "promotion of the general interest of the Union in mind".

Sir Julian was sent to Brussels to fill the vacancy left when former commissioner Lord Hill of Oareford resigned in the wake of the referendum.

A career diplomat, he took up an ambassadorial posting in Paris in February this year, having previously served as ambassador to Ireland from 2009 to 2011.

He spent five years in Brussels from 2004-09, first as part of the UK representation to the EU and then as chief of staff in the office of the British Commissioner, serving under Lord Mandelson and Lady Ashton.

A Downing Street spokesman said: "We welcome this decision by the President of the European Commission.

"The UK will continue to fulfil our rights and obligations as a member state until we leave the EU and the Prime Minister has been clear that we will be an active player, so it is right that we should continue to have a Commissioner role.

"Security is a vital issue for all member states and co-operation across the EU can help to better protect us all from the range of threats we face.

"The President called the Prime Minister yesterday evening to inform her of his decision. We now look forward to Sir Julian being confirmed in the role."